guanethidine (Ismelin, Santensin)

Introduction

Tradename: Ismelin.

Indications

treatment of moderate to severe hypertension

Contraindications

• pheochromocytoma
• concurrent administration of MAO inhibitor

Caution:

• use with caution in the elderly
• frequent occurrence of orthostatic hypotension

pregnancy category = c

safety in lactation = -

Dosage

• adults
  • start 10 mg PO QD
  • increase by 10 mg/day at intervals of 5-7 days
  • usual 25-50 mg/day
• children
  • start: 0.2 mg/kg/day up to 10 mg
  • increase by 0.2 mg/kg every 1-3 weeks
  • maximum dose: 3 mg/kg/day

Tabs: 10 & 25 mg.

Adverse effects

• common (> 10%)
  • palpitations, chest pain, peripheral edema, fatigue, headache, faintness, drowsiness, confusion, increased bowel movements, pain from flatulence, constipation, anorexia, weight gain/loss, nocturia, polyuria, retrograde ejaculation, paresthesia, muscle ache (especially leg cramps), backache, arthralgia, visual disturbances, shortness of breath, cough
• less common (1-10%)
  • orthostatic hypotension, psychologic disturbance, depression, sleep disorder, glossitis, nausea/vomiting xerostomia, hematuria
• uncommon (< 1%)
  • syncope, angina
• other
  • fluid retention
  • diarrhea

• drug adverse effects of antihypertensive agents

Drug interactions

• tricyclic antidepressants (TCA), antihistamines, ephedrine interfere with the action of guanethidine
• phenothiazines
• anorexiants
• haloperidol
• maprotiline
• methylphenidate
• MAO inhibitors

• drug interaction(s) of NSAIDs & antihypertensives

Mechanism of action

• replaces norepinephrine within secretory granules of adrenergic neurons

More general terms

• adrenergic neuron inhibitor

Component of

• guanethidine/hydrochlorothiazide; guanethidine/HCTZ (Esmil)

Database

• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=3518
• PubChem: http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=88123